The effectiveness of Pre-Exposure Prophylaxis (PrEP) for reducing HIV transmission is strongly dependent on adherence, which is influenced by individual, social, and structural factors. We propose a social network-based intervention to promote PrEP adherence among transgender women (TW) in Lima, Peru: 1) Formative research. To optimize content for a PrEP adherence intervention, we will conduct semi- structured interviews and focus groups. Results will be used to refine the PrEP adherence intervention. 2) To conduct an open evaluation of a social network-based PrEP adherence intervention for TW in Peru. The intervention model will be piloted with a small group of 5-10 TW. Data will be used to finalize the study design and assessment tools for a pilot randomized controlled trial (RCT). 3) To conduct a pilot RCT of a social network-based PrEP adherence intervention for TW in Peru. We plan to randomize 8 social network-based clusters of TW that to either a network-based PrEP adherence intervention or standardized PrEP adherence counseling. The primary outcome will be PrEP adherence. The intervention will use a combination of individual counseling, group workshops, social media-based network interactions, and practical support tools to promote PrEP adherence among TW. Individual Counseling: Participants will complete two biweekly counseling sessions addressing PrEP use and HIV prevention. The goals of individual counseling are to introduce PrEP as an HIV prevention tool and address basic issues of PrEP adherence as part of a comprehensive HIV prevention strategy. Group Workshops. Group workshops will establish a common understanding of PrEP as a central component of comprehensive HIV prevention, address the importance of PrEP adherence, develop practical strategies to support adherence, and generate and maintain norms of HIV prevention and PrEP adherence within the peer group. Biweekly maintenance meetings will address ongoing issues related to PrEP use and adherence. Social Network Interactions. The social network component of the intervention will include structured social media platforms to educate, motivate, and promote discussions of PrEP adherence within the participant network, unstructured participant-generated interactions to articulate and reinforce newly developed social norms within the network, and practical tools to support daily adherence. PrEP Use. Participants will be provided with daily Truvada for the 6-month study period. Assessment Procedures, Timing and Measures. There will be three major assessment points: baseline, short-term outcome (3 month), and long-term outcome (6 month). The primary outcome of the intervention will be a comparison of PrEP adherence in the intervention and control groups. Findings will be used to support an NIH-funded R01 proposal using social networks of TW and social media technologies to generate, implement, and reinforce new social norms of PrEP adherence, sexual risk behavior, and HIV prevention.